Quake risk higher than estimated
Muscat: Recent research has revealed that the Makran Subduction Zone (MSZ) is more prone to earthquakes and tsunami hazards than previously thought.
The research — which can currently be viewed online on the Geophysical Research Letters website, and which will be published soon — has been conducted by scientists from the University of Southampton and the Pacific Geoscience Centre, Canada.
According to it, an earthquake of the same magnitude as the 2004 Sumatra earthquake can happen anytime in the MSZ, which lies in Balochistan along the southwestern coast of Pakistan, where the oceanic crust of the Arabian Plate is subducting beneath the continental crust of the Eurasian Plate.
Around 227,898 people died in 14 countries when an earthquake hit the Indian Ocean on December 26, 2004, with its epicentre off the western coast of Sumatra, Indonesia. It was one of the deadliest natural disasters recorded in history. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.
According to the report, a copy of which is available with Times of Oman, scientists had previously underestimated the potential risk of undersea earthquakes — and the associated tsunamis — near the western part of the Indian Ocean, but this study reveals that Pakistan, Iran, Oman, and India's coastlines are prone to even greater dangers.
Speaking to Times of Oman, Dr Lisa McNeill, one of the researchers of Ocean and Earth Science, National Oceanography Centre, Southampton, said that the deeper sediments are more compressed and warmer and, as a result, the shallowest part of the subduction zone fault is potentially capable of slipping during an earthquake. Speaking from United Kingdom, she said, "When combined, all these factors increase the risk of major earthquakes in the MSZ, pushing the magnitude up to between 8.7 and 9.2."
Echoing similar sentiments, Dr Gösta Hoffmann, associate professor, Quaternary Geology & Geomorphology, GUtech, said that 1945 earthquake was not the worst case. "We are working to define this case," he said.
Regarding the effects on Oman, Dr Lisa McNeill stressed that this study highlights merely the potential for a large earthquake and tsunami. "We cannot say that an earthquake will definitely take place. Moreover, as with all other earthquakes, we cannot predict when an earthquake will take place. That is all the more true here because there isn't much information about earthquakes in MSZ. Studies are now being conducted by scientists — including those in Oman — and we hope that this study will lead to more studies into the history of earthquakes and tsunamis in the region and will, consequently, be taken into account for regional hazard mitigation purposes," she said.
If a large magnitude subduction zone earthquake (say magnitude > 8) took place on the MSZ, a tsunami wave would be generated. "The most intense the earthquake, the larger the resulting tsunami and, therefore, the greater the potential damage to coastlines, even those further away from the subduction zone itself.
"This type of an event could generate a destructive tsunami on the Oman coastline. In 1945, a magnitude-8.1 earthquake occurred in the subduction zone and generated a tsunami that affected coastlines. We don't exactly know the nature of that earthquake — but we think it could be the same type that our published study describes.
"The 1945 earthquake generated a small tsunami on the Oman coastline causing only minor damage," she added.
The study suggests that even larger earthquakes could occur in the subduction zone, and these could be even more damaging than the 1945 event. This study is important scientifically because the geological characteristics of the MSZ — very thick sedimentation, partly a result of erosion in the Himalaya — made a very large earthquake seem unlikely. "The zone is also quite quiet in terms of earthquakes. Geologists believed that the sedimented part of the subduction zone fault slipped quietly without causing earthquakes. But recent earthquakes, including the Sumatra 2004 event, suggest this isn't always true. We think that when the sediments are very thick they may become very hot and strong at their base.
"This is where the major fault develops and the deep sediments may be strong enough to slip, resulting in an earthquake. This coupled with the wide margin because of the low dip of the subducting plate creates a large potential area that could rupture during an earthquake. So recent earthquakes such as Sumatra 2004 and Japan 2011 have made us re-evaluate the earthquake process at subduction zones, and the MSZ is certainly one place to look at again," she added. TimesOfOman